Polishing glass



July 18, 1961 E. H. GLASGOW 2,992,521

POLISHING GLASS Filed May 25, 1960 FIG. I

INCOMPLETE FINISH F'IG.2

COM FLETE INISH United rates ifiatent 2,992,521 POLISHING GLASS Earl H. Glasgow, Crystal City, Mo., assignor to Pittsburgh Plate Glass Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed May 25, 1960, Ser. No. 31,595 Claims. (Cl. 51-283) This invention relates to a method for polishing plate glass, and particularly to the method in which plates of glass are conveyed on cars, tables or other carrier apparatus beneath a series of polishing runners wherein successive major surfaces are polished, one at a time.

In the method for manufacturing polished plate glass to which this invention is adaptable, the usual procedure is to embed discrete rough rolled glass sheets in plaster of Paris on tables or lay the sheets on cloth covered tables which are then joined together and conveyed in a continuous fashion through grinding apparatus wherein the upper major surface is ground by a slurry of sand and water, producing what is known as a smooth, and then through polishing apparatus wherein the smooth is surfaced by a rouge and copper as water slurry. Frequently, glass sheets become broken while on the tables, especially while passing through the grinding apparatus and before being presented to the polishing apparatus. Because the tables are connected together for the entire surfacing operation and due to time limitations, the tables with the broken sheets cannot be removed from the line so that the broken sheet is conveyed through the polishing apparatus.

Contact of the polishing runners with a broken sheet of glass causes damage to the runners and also, because of glass chips becoming embedded in the runner polishing surfaces causes damage to subsequent plates of glass. Thus, to eliminate these results, which require replacement of the runner polishing surfaces and perhaps a loss of a large quantity of product, the usual procedure has been to sequentially vertically lift the polishing runners from polishing contact in advance of the broken sheet and then vertically lower the polishing runners to polishing contact after the broken sheet has passed. This procedure protects the runner polishing surfaces but results in the sheets leading and trailing the broken sheets being only partially polished with a resultant decrease in saleable product.

It has now been found possible to avoid lifting the runners, damage to the runners and glass sheets, and to increase the yield of saleable product by masking any breaks which may occur prior to presentation to the polishing apparatus. This is accomplished by applying a pressure sensitive tape to cover the breaks in the glass sheets. Tape of this type can be quickly applied without interrupting the surfacing operation. Of course, the glass immediately beneath the tape is not polished, but substantially the remainder of the glass sheet is, so that not only are the leading and trailing sheets completely polished and thus saleable, but large portions of the broken sheets are completely polished and may be cut into saleable sizes of plate glass.

Therefore, the primary object of this invention is to provide a method of treating breaks in glass plates prior to presentation to polishing apparatus for surfacing, so as to eliminate damage to the surfacing equipment and increase the yield of the product.

Other objects, features and advantages of the invention will be apparent from the following description when taken with the accompanying drawing, in which;

FIG. 1 represents successive glass plates as they continuously are conveyed through polishing apparatus with a break indicated therein and the results obtained when following the conventional procedure; and

FIG. Zrepresents successive glass plates as they continuously are conveyed through polishing apparatus with a break indicated therein repaired in accordance with the teachings of this invention and the results thus obtained.

Looking at FIG. 1, we see a series of glass plates or sheets 1, 2, 3, 4 and 5 advancing through polishing apparatus in the direction indicated by legend and arrow. The polishing apparatus, as for example those with feltfaced runners, or the glass plate supporting tables and conveying means are not illustrated because they are conventional in construction and well known in the art. A break, identified as 10 is indicated in sheet 3. Breaks of this nature are generally irregular and occur at random in a plate, so that the break indicated is only for purposes of illustration and description. As will be noted from legends, a portion of leading plate 4 after passing through the polishers has a normal finish, but a portion has a poor finish because the polishing runners must be raised from polishing contact before the broken plate passes thereunder. Therefore, while plate 4- may be perfect in dimensions, only the portion with the normal finish is saleable, the remaining portion being unsalcable and relegated to cullet. Plate 3, with the break, is completely unsaleable, and trailing plate 2 will be only partially polished because the polishing runners must be lowered into polishing contact after plate 3 with the break passes thereunder. As will be readily understood, a large quantity of finished product is thereby lost.

FIG. 2 shows a like series of glass sheets or plates 1A, 2A, 3A, 4A, and 5A being conveyed through the polishing apparatus in. the direction indicated by legend and arrow. As in the case of FIG. 1, the polishing apparatus and supporting and conveying tables are not illustrated because they are conventional and well known in the art.

The break 11 is shown in broken lines and is masked by relatively thin strip material 12, such as pressure sensitive tape. When the break is irregular, short pieces of the tape are employed, and the entire break is masked. Also, more than one layer of strip material tape may be used as when there are multiple breaks closely adjacent one another because overlaps do not affect the operation. Excellent results have been obtained with an aluminum pressure sensitive tape 2 inches wide and on the order of 0.005 inch thick. This tape adheres to the glass plate without necessity for a glass surface cleaning treatment. Application is made by hand or other manually operated applicator means between the grinding apparatus and the polishing apparatus.

The results obtained by masking the breaks with respect to the product are clearly shown in FIG. 2. The only areas of the plate not polished are those beneath the tape. The leading and trailing glass sheets are completely finished or polished and the broken plate excluding the taped portion is completely polished. Thus, with a predetermined vertical relationship between polishing runners and glass being maintained throughout the polishing operation and the masking of the breaks from contact with the runners, it is possible to salvage portions of the broken sheet and to completely use the leading and trailing sheets. This procedure results in a more continuous polishing process because of no interruption or" the polishing process, a savings in repair and/ or replacement of polishing surfaces because glass chips are not exposed to polishing surfaces and do not become embedded therein, so as to damage other glass sheets, and a greateryield of saleable product because more glass is completely polished.

I claim:

1. In a method for polishing glass wherein a plurality of supported glass sheets are continuously conveyed in series through a polishing apparatus and are contacted by a plurality of polishing runners adapted to be lifted from and returned into contact with the glass sheets as they are conveyed and said glass sheets are characterized by randomly broken sheets randomly occurring within the plurality requiring lifting and returning the polishing runners from and to contact with the broken sheets and the immediately adjacent leading and trailing sheets to avoid damage to the runners, thereby incompletely polishing portions of said leading and trailing sheets and all of said broken sheets, the improvement which comprises adhering a strip material to said broken sheets.-

over breaks therein and continuously contacting said broken sheets and the immediately adjacent leading and trailing sheets with said runners thereby avoiding damage to said runners and completely polishing all glass surfaces exposed to said runners.

2. A method as recited in claim 1 wherein said strip material is a pressure sensitive tape.

3. A method as recited in claim 1 wherein said strip material is a pressure sensitive metal tape.

4. A method as recited in claim 3 wherein said pressure sensitive tape is of aluminum.

5. A method as recited in claim 1 wherein said strip material is 0.005 inch thick.

6. In a method for polishing glass wherein a plurality of supported glass sheets are continuously conveyed in series through a polishing apparatus and are contacted by a plurality of polishing runners adapted to be lifted from and returned into contact with the glass sheets as they are conveyed and said glass sheets are characterized by randomly broken sheets randomly occurring within the plurality requiring lifting and returning the polishing runners from and to contact with the broken sheets and the immediately adjacent leading and trailing sheets to avoid damage to the runners, thereby incompletely polishing portions of said leading and trailing sheets and all of said broken sheets, the improvement which comprises masking said breaks from contact with said polishing runners prior to presentation to said polishing runners and continuously contacting said broken sheets and the immediately adjacent leading and trailing sheets with said runners thereby avoiding damage to said runners and completely polishing all glass surfaces exposed to said runners.

7. A method for polishing a glass sheet having breaks therein wherein a polishing runner having a felt polishing face which rubs a surface of said glass and is subject to damage by contact with said breaks, the improvement which comprises masking said breaks from contact with said polishing felt and contacting said surface of said glass with said polishing felt while maintaining a predetermined vertical relationship of said polishing felt and said glass and thereby avoiding damage to said felt.

8. The method for polishing a glass sheet as recited in claim 7 wherein masking said breaks comprises adhering a pressure sensitive tape to said glass over said breaks.

9. A method for polishing glass sheets subject to breaks therein wherein a plurality of polishing runners having felt polishing faces which rub a surface of said glass and are subject to damage by contact with said breaks, the improvement which comprises masking said breaks from contact with said polishing felts and contacting said surface of said glass with said felts while maintaining a predetermined vertical relationship of said felt and said glass thereby avoiding damage to said felts.

10. The method as recited in claim 9 wherein masking said breaks comprises adhering a pressure sensitive metal tape to said glass completely covering said breaks.

No references cited.

UNITED STATESPATENT. OFFICE CERTIFICATE OF CORRECTION Patent No. 2,992,521 July 18 1961 Earl H. Glasgow It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent shouldread as corrected below Column 1, line. 23 for "copper as." read copperas Signed and sealed this 24th day of July 1962 (SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Atteating Officer Commissioner of Patents 

